Conventional aircraft wings comprise a wing box with front and rear spars. Upper and lower wing covers are attached to the spars and extend between them to form the upper and lower boundaries of the wing box. Leading and trailing edge structures, such as panels or D-nose covers, are typically attached to the upper and lower covers with butt straps. FIGS. 1 and 2 illustrate conventional butt-strap arrangements.
An upper wing cover 1 is attached to a fixed leading edge structure 2 with a butt-strap 3, a pair of bolts 4, 5 and nuts 9, 10. The butt-strap 3 comprises upper and lower horizontal portions 6, 7 which are joined by a vertical portion 8. The lower portion 6 engages with the internal surface of the cover 1, while the upper portion 7 engages with the internal surface of the fixed leading edge structure 2.
To achieve a smooth aerodynamic surface, the external surface of the structure 2 and the external surface of the cover 1 must be aligned with each other within a strict tolerance range. To ensure that the alignment criteria are met, a packer 11 may be added between the internal surface of the structure 2 and the upper portion 7 of the butt-Strap, as shown in FIG. 1. Alternatively, as shown in FIG. 2, a packer 12 may be added between the internal surface of the cover 1 and the lower portion 6 of the butt-strap. However, as the butt-straps 3 are typically fitted in various strips across the whole span of the wing, this process can be difficult and time consuming. It may also be necessary to hand fettle the structure 2 to match the cover 1 during assembly. This adds further complexity to the process. In addition, loads can only be channelled from the structure 2 into the spar (not shown) via the cover 1.